1. Field of the Invention
The present invention relates to a safety device which automatically and independently mechanically triggers a total or partial closure of a guard or safety member, such as valve or cock, in order to prevent fluid flow through a duct such as a pipe or conduit when the velocity of the fluid circulating in duct attains a determined value considered as dangerous.
2. History of the Art
Most forced conduits used in hydro-electric installations are provided with guard members, such as ball valves or butterfly valves. In the event of an accident in the conduit or the other equipment which is fluid communication with the conduit, such guard members are closed in order to stop the uncontrolled flow of fluid therethrough.
In general, when the fluid conveyed in a duct escapes the control of the installation, for example, by a pipe bursting, an increase in the flow velocity of this fluid results. Such increase in flow velocity is used and detected to control the closure of the guard member.
Known devices for ensuring this automatic safety are numerous. In general, they are detection devices employing turnstile, laser ray, magnetic field, or other devices, which are connected to a measuring chain and to a power device which is connected to an outside energy supply.
Such devices are complex and expensive as they utilize elaborate control systems including electronics, high-precision mechanics and the like. They necessitate the use of a measuring chain which requires continuous maintenance. Further, and in particular such systems, necessitate the use of an outside energy source, for example electricity, which considerably affects their reliability.
In order best to satisfy the requirement of simplicity and quality desired for this type of safety device, as well as to create an independence from any outside energy source, so-called "blade tripping" devices have already been used. A device of this type comprises a blade mounted in pendulum fashion in the stream of fluid and maintained perpendicular to the stream by a balancing counterweight. The blade is therefore subjected to the hydrodynamic forces created by the flow of the fluid (water in the majority of cases). When the hydrodynamic moment on the blade attains a predetermined value, the blade rotates a spindle with which it is connected. A lever device connected with this spindle then mechanically causes closure of the duct guard or valve member.
It will be readily appreciated that the mechanical power transmitted by the tipping of this blade is weak. The use of this power to trigger the closure of the guard member therefore calls upon sophisticated lever devices, which require delicate adjustment and maintenance, with the result that the system becomes overly complex and subject to failure. Furthermore, the pressure exerted by the fluid on the blade decreases when the blade inclines rearwardly. As it is moved by the fluid and thus tends to return to its starting position.
Additionally, the blade tripping device presents the other following drawbacks:
the device for detecting the velocity of the fluid and the device for triggering the closure of the guard member are positioned at the same place or location along a fluid conduit which may be a position subject to disturbance. To this end, it would be advantageous to have a detection device placed remote from this place or location; PA0 the blade is gradually covered with impurities, which increases its weight and its surface area and therefore falsifies the initial adjustment; PA0 the device is sensitive to fluctuations in pressure, which brings a risk of untimely triggering; PA0 the device uses springs, which may function poorly; PA0 the device is fairly cumbersome; PA0 once in position, the device can operate only for one direction fluid flow; and PA0 the velocity detection device comprises moving mechanical parts.